Indian Journal of Plant Sciences ISSN: 2319–3824(Online) An Open Access, Online International Journal Available at http://www.cibtech.org/jps.htm 2016 Vol.5 (1) January-March, pp.70-86/Srivastava et al. Review Article © Copyright 2014 | Centre for Info Bio Technology (CIBTech) 70 ON THE IMPORTANCE OF DIATOMS AS ECOLOGICAL INDICATORS IN RIVER ECOSYSTEMS: A REVIEW *Prateek Srivastava 1 , Jyoti Verma 2 , Sarika Grover 1 and Ambrina Sardar 1 1 Amity Institute of Environmental Sciences, Amity University, Noida 201 303 2 Department of Zoology, University of Allahabad, Allahabad 211 001 *Author for Correspondence ABSTRACT Ecological indicators have widespread appeal to scientists, environmental managers, and the general public at large. They have long been used to detect changes in nature, but the scientific maturation in indicator development has occurred mainly in the past twenty years. Currently, indicators are primarily used to assess the condition of the environment, as early-warning signals of ecological problems and as barometers for trends in ecological resources. The diatoms (Bacillariophyceae) comprise a ubiquitous, highly successful and distinctive group of unicellular algae which have served as the most valuable indicator for the ecological assessment of rivers round the globe for the past fifty years. The European Water Framework Directive has required them to be used for assessing the ecological quality of water resources since the year 2000. Diatoms are highly sensitive to changes in nutrient concentration, organic pollution and aquatic productivity. This paper attempts to focus on the rationale for the use of diatoms as bio monitors. It incorporates various diatom indices developed for the eco-assessment of rivers from various regions of the world. In India, many research papers have been published with respect to bio monitoring by plankton and macro invertebrates, yet the diatoms have been rarely used for bio assessment of major rivers. Keywords: Bacillariophyceae, Biomonitors, Diatom Indices, Eco-Assessment, River Ecosystems INTRODUCTION The rapid increase in anthropogenic activities threatens the sustainability of services provided by ecosystems Millennium Ecosystem Assessment, (2005), and some of the planetary boundaries for sustainable use have already been exceeded (Rockstrom et al., 2009). Rivers are a paradigmatic example of this situation: they provide key services to society, harbour a large part of the world biodiversity, but are amongst the most endangered ecosystems of the world (Hering et al., 2006; UNEP, 2007; Elosegi & Sabater, 2013). All around the world there are urgent demands for comprehensive methodological approaches to evaluate the actual state of these ecosystems and to monitor their rate of changes (Li et al., 2010). So far as the health of rivers in India is concerned, river pollution has now reached to a point of crisis due to geometric increase in human population coupled with rapid urbanization, industrialization and agricultural developments (Trivedi et al., 2008). The situation warrants immediate reprisal through radically improved water resources and water quality management strategies. The Water (Prevention and control of pollution) Act, 1974 emphasizes on the wholesomeness of the water bodies and under its sections stresses on protection of human health and living creatures. Similarly the recently notified Environmental Policy, 2006 (MoEF, 2006) also strongly emphasizes on protection of wildlife, fisheries and other living beings. Bio Monitoring: An Appealing Tool for Water Quality Assessment Water quality evaluation based on physical, chemical and bacteriological measurements commonly form the basis of monitoring as they have been known to provide a complete spectrum of information for proper water management (Li et al., 2010). However, physical and chemical methods restrain the assessment of water conditions to that particular moment when the measurements are taken and thus, do not provide an integrated reflection of the water quality. In addition, even continuous chemical monitoring and data logging can miss events that might